Age Difference Calculator

What Is an Age Difference Calculator?

An age difference calculator (also called a date difference or date duration calculator) tells you the exact time span between two dates in years, months, and days. Unlike a simple day counter, it breaks down the result into calendar units that are easy to interpret—for example, "12 years, 3 months, and 5 days"—so you can quickly see how far apart two events are. This is useful for age gaps between people, project timelines, contract periods, or any two dates you need to compare.

Our tool calculates the difference between two dates instantly and shows both the breakdown (years, months, days) and the total number of days between them. Everything runs in your browser, so your dates are never uploaded or stored anywhere.

How We Calculate Years, Months, and Days

We use an iterative calendar algorithm so the result matches the calendar exactly. First, both dates are normalized to noon to avoid daylight saving time edge cases. Then we determine which date is earlier and which is later. We count how many full calendar years fit between them, then how many full months remain, and finally the remaining days. Total days is computed separately from the millisecond difference between the two dates.

This approach correctly handles leap years (including the rule that century years are only leap years if divisible by 400) and variable month lengths. For example, from January 31 to February 28 in a non-leap year, the result is 28 days—not "one month"—because February has only 28 days. From January 31 to March 1 in a non-leap year, the result is 1 month and 1 day. You get calendar-accurate results every time.

Examples: Real Scenarios

Age gap between two people

Person A born March 15, 1990; Person B born July 20, 1995. The difference is 5 years, 4 months, and 5 days. Our age gap calculator gives you this breakdown so you can quickly compare ages or plan events.

Project or contract duration

Start date January 1, 2023; end date April 15, 2024. The difference is 1 year, 3 months, and 14 days (or 471 total days). Useful for reporting how long a project ran or how many years and months a contract covered.

Same calendar day

If you pick the same date for both fields, the result is 0 years, 0 months, 0 days (0 total days). The tool handles same-date and adjacent-day cases correctly.

Age Difference vs Total Days Explained

The years, months, and days breakdown is a human-friendly way to read the span: "2 years, 6 months, 10 days" is easier to grasp than "921 days." The total days figure is the exact number of 24-hour periods between the two dates and is useful for calculations (e.g. interest, billing cycles) or when you need a single number. Our calculator shows both so you can use whichever format fits your need.

Why Use a Browser-Based Calculator?

A browser-based age difference calculator runs entirely on your device. Your dates are never sent to a server, so there is no privacy risk and no delay. Results appear as soon as both dates are selected, and the tool works offline once the page is loaded. There are no signups, no ads over the inputs, and no usage limits—ideal for quick checks at work, in school, or at home.

Common Questions About Date Differences

How many days between dates? The calculator shows total days below the main result. Years between two dates? The first number in the result is the full years. Does it work across leap years? Yes—February 29 is handled correctly in leap years, and the iterative algorithm ensures accurate years, months, and days for any pair of dates. For more date and time tools, try our Age Calculator, Date Calculator, Time Calculator, and Time Zone Converter.